Vitol E&P has held a 22.06% indirect working interest in the offshore Marine XI licence since 2006 and acquired a 29.72% non-operated interest in the adjacent Marine XIV licence in 2008. Both blocks are operated by SOCO Exploration and Production Congo Ltd and contain legacy discoveries including the Viodo field.
The blocks are located in the offshore waters of the Lower Congo Basin. Marine XI covers 1,400 sq km and lies in shallow water adjacent to the coast at depths of up to 110 metres. Marine XIV comprises three discontinuous sections over a total area of 265 sq km in slightly deeper water – ranging from 100 to 150 metres.
The licences lie in a mature hydrocarbon province surrounded by producing fields and discoveries. Reservoir potential occurs at multiple levels with the stratigraphy being subdivided into pre-salt and post-salt formations – the salt being of Aptian age. Previous exploration and development has targeted the post-salt formations, leaving the pre-salt section under-explored. The reservoir lithologies range from immature alluvial sandstones and conglomerates to shallow lacustrine and marine carbonates.
The Viodo field was discovered in the mid-1980s in the pre-salt Toca carbonate formation. As the reservoir rock is heterogeneous and complex, appraisal of the reservoir has historically proved difficult.
In 2009, the VIM-4 appraisal well was successfully drilled and gathered good quality log, core and well-test data to further evaluate the field and the wider Toca play. The well flowed 30º API crude at a rate of approximately 2,700 bopd. The well data has been incorporated into the Viodo static and dynamic models to evaluate the development potential of the field and the wider Toca play. A further commitment exploration well – Mindou Marine-1 - was drilled on the licence in 2011, but abandoned as a dry hole.
A novel multi-azimuth seismic survey was acquired in 2009 over the Marine XIV block to improve the seismic character and imaging of deeper pre-salt structures, which overlap the block boundary into the western area of Marine XI. A commitment exploration well – Makouala Marine-1 was drilled at the end of 2011 in a post-salt structure, but was unsuccessful.
Arbitrary seismic line through Marine XI/Marine XIV blocks showing pre- and post-salt reservoir structures